Remove a spike of memory usage in ScrubDisposablePass. (#2978)

ScrubDisposablePass consumed a lot of memory only for a moment.
This was because disposalElementsAttr was kept after converting to denseElementsAttr.
This PR removes the spike by deleting disposalElementsAttr just after each conversion.
---------

Signed-off-by: Haruki Imai <[email protected]>

src/Dialect/ONNX/ElementsAttr/DisposablePool.cpp

@@ -114,17 +114,18 @@ void DisposablePool::scrub(ModuleOp moduleOp, OpAttrDictionary opsAttrs) {
       return llvm::make_range(batchBegin, batchEnd);
     };
     // Parallel worker body: Fetch and process batches until there are no more.
-    auto work = [&fetchBatch](size_t threadNumber) {
+    auto work = [&fetchBatch, &translationMutex](size_t threadNumber) {
       for (;;) {
         auto batch = fetchBatch();
         if (batch.empty())
           break;
         for (auto &[id, translation] : batch) {
           auto &[disposable, dense] = translation;
           dense = disposable.toDenseElementsAttr();
-          // TODO: Consider calling disposable.dispose() here to free up memory
-          //       on the go to make memory available to create the next
-          //       DenseElementsAttr. In that case should we lock mutex?
+          {
+            const std::lock_guard<std::mutex> lock(translationMutex);
+            disposable.dispose();
+          }
         }
       }
     };